As an analyzer that analyzes an amount of a component contained in a sample, an automatic analyzer is widely used, in which the amount of the component is determined from a relation between absorbance and a concentration in accordance with the Lambert-Beer law by irradiating a sample or reaction solution of a mixture of the sample and a reagent with light from a light source, measuring transmitted light quantity at a single or a plurality of wavelength (s) as a result obtained by the irradiation, and calculating an absorbance (see Patent Document 1).
In such a device, many reaction containers retaining the reaction solution are circumferentially arranged on a reaction disk which repeatedly rotates and stops, and time-dependent change of the absorbance is measured at a constant time interval for about minutes during the rotation of the reaction disk by a transmitted-light measuring unit previously arranged. After the measurement is terminated, the reaction containers are cleaned by a cleaning mechanism and are used for the re-analysis.
As the reaction of the reaction solution, roughly two types of reactions including color reaction between a substrate and an enzyme and agglutination reaction between an antigen and an antibody are used.
The former one is biochemical analysis having test items which are LDH (Lactate Dehydrogenase), ALP (Alkaline Phosphatase), AST (Aspartate Aminotransferase), and others. The latter one is immuno-analysis having tested items which are CRP (C-reactive protein), IgG (Immunoglobulin G), RF (Rheumatoid factor), and others.
A blood concentration of a measurement substance measured in the immuno-analysis of the latter one is low, and therefore, a highly sensitive detection system is required. For example, the high sensitivity has been advanced by a latex agglutination method that quantifies the amount of the component contained in the sample by: using a reagent which is obtained by sensitizing (coupling) an antibody onto surfaces of latex particles, irradiating a reaction solution with light upon the agglutination of the latex particles by antigen-antibody reaction with an antigen contained in the sample, and measuring the quantity of the light transmitted without being scattered by latex agglutinate.
Further, as an automatic analyzer, the high sensitivity has been attempted by measuring not the transmitted light quantity but the scattered light quantity.
Incidentally, in achieving the high sensitivity, even drift of light quantity data caused by slight variation in a temperature in the device becomes a large problem when change of minute light quantity is detected at high sensitivity. It is considered that the drifts of the light quantity data are roughly categorized into (1) drift of a light source, (2) drift of an electric circuit system, and (3) drift caused by thermal deformation of an optical system. Regarding (1) the drift of the light source, a technique of monitoring the irradiation light quantity for the correction (see Patent Document 2) is known. Regarding (2) the drift of the electric circuit system, a technique of suppressing the circuit-derived drift by controlling a temperature in a circuit board storage is known (see Patent Document 3).